Systems and methods for backoff counter handling in license assisted access

ABSTRACT

An evolved NodeB (eNB) for scheduling multiple Licensed-Assisted Access (LAA) cells is described that includes a processor and memory in electronic communication with the processor. Instructions stored in the memory are executable to perform clear channel assessment (CCA) detection and obtain a channel status at a configured Licensed-Assisted Access (LAA) secondary cell (SCell). The instructions are also executable to manage a counter. The instructions are further executable to determine whether the counter is reduced or suspended if the channel is sensed to be idle. The instructions are additionally executable to reduce the counter if determined, otherwise suspend the counter and move to a next channel sensing.

RELATED APPLICATIONS

This application is related to and claims priority from U.S. ProvisionalPatent Application No. 62/201,042, entitled “SYSTEMS AND METHODS FORBACKOFF COUNTER HANDLING IN LICENSE ASSISTED ACCESS,” filed on Aug. 4,2015, which is hereby incorporated by reference herein, in its entirety.

TECHNICAL FIELD

The present disclosure relates generally to communication systems. Morespecifically, the present disclosure relates to systems and methods forbackoff counter handling in licensed assisted access (LAA).

BACKGROUND

Wireless communication devices have become smaller and more powerful inorder to meet consumer needs and to improve portability and convenience.Consumers have become dependent upon wireless communication devices andhave come to expect reliable service, expanded areas of coverage andincreased functionality. A wireless communication system may providecommunication for a number of wireless communication devices, each ofwhich may be serviced by a base station. A base station may be a devicethat communicates with wireless communication devices.

As wireless communication devices have advanced, improvements incommunication capacity, speed, flexibility and/or efficiency have beensought. However, improving communication capacity, speed, flexibilityand/or efficiency may present certain problems.

For example, wireless communication devices may communicate with one ormore devices using a communication structure. However, the communicationstructure used may only offer limited flexibility and/or efficiency. Asillustrated by this discussion, systems and methods that improvecommunication flexibility and/or efficiency may be beneficial.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating one implementation of one or moreevolved NodeBs (eNBs) and one or more user equipments (UEs) in whichsystems and methods for licensed assisted access (LAA) may beimplemented;

FIG. 2 is a flow diagram illustrating a method for scheduling multipleLAA cells by an eNB;

FIG. 3 illustrates an example of a LAA subframe burst transmission;

FIG. 4 illustrates an example of LAA coexistence with other unlicensedtransmissions;

FIG. 5 illustrates an example of a hidden terminal issue with unlicensedtransmissions;

FIG. 6 illustrates examples of simultaneous LTE transmissions on asingle carrier;

FIG. 7 is a flow diagram illustrating a method for distributed LAAcontention access without coordination among LAA cells;

FIG. 8 is a flow diagram illustrating a method for simultaneous LAAtransmissions with coordinated LAA cell operation;

FIG. 9 is a flow diagram illustrating a method for coordinatedtransmission when multiple LAA cells obtain channel access;

FIG. 10 is a flow diagram illustrating a method for coordinated LAAoperation with hidden terminal avoidance;

FIG. 11 is a flow diagram illustrating a method for LAA state transitionwith variable length backoff;

FIG. 12 illustrates examples of issues with initial clear channelassessment (ICCA) deferring after a backoff counter reaches zero;

FIG. 13 illustrates an example of how an LAA cell can transmit at anygiven time within a zero counter defer period;

FIG. 14 is a flow diagram illustrating another method for schedulingmultiple LAA cells by an eNB;

FIG. 15 is a flow diagram illustrating yet another method for schedulingmultiple LAA cells by an eNB;

FIG. 16 illustrates various components that may be utilized in a UE;

FIG. 17 illustrates various components that may be utilized in an eNB;

FIG. 18 is a block diagram illustrating one implementation of a UE inwhich systems and methods for scheduling multiple LAA serving cells maybe implemented; and

FIG. 19 is a block diagram illustrating one implementation of an eNB inwhich systems and methods for scheduling multiple LAA serving cells maybe implemented.

DETAILED DESCRIPTION

An evolved NodeB (eNB) for scheduling multiple Licensed-Assisted Access(LAA) cells is described that includes a processor and memory inelectronic communication with the processor. Instructions stored in thememory are executable to perform clear channel assessment (CCA)detection and obtain a channel status at a configured Licensed-AssistedAccess (LAA) secondary cell (SCell). The instructions are alsoexecutable to manage a counter. The instructions are further executableto determine whether the counter is reduced or suspended if the channelis sensed to be idle. The instructions are additionally executable toreduce the counter if determined, otherwise suspend the counter and moveto a next channel sensing.

The eNB may determine whether or not the eNB performs a transmission, ifthe counter reaches zero. The eNB may perform the transmission ifdetermined, otherwise the eNB may suspend the transmission and performan additional channel sensing for the transmission.

A method for an eNB for scheduling multiple LAA cells is also described.The method includes performing CCA detection and obtaining a channelstatus at a configured LAA SCell. The method also includes managing acounter. The method further includes determining whether the counter isreduced or suspended if the channel is sensed to be idle. The methodadditionally includes reducing the counter if determined, otherwisesuspending the counter and moving to a next channel sensing.

The 3rd Generation Partnership Project, also referred to as “3GPP,” is acollaboration agreement that aims to define globally applicabletechnical specifications and technical reports for third and fourthgeneration wireless communication systems. The 3GPP may definespecifications for next generation mobile networks, systems and devices.

3GPP Long Term Evolution (LTE) is the name given to a project to improvethe Universal Mobile Telecommunications System (UMTS) mobile phone ordevice standard to cope with future requirements. In one aspect, UMTShas been modified to provide support and specification for the EvolvedUniversal Terrestrial Radio Access (E-UTRA) and Evolved UniversalTerrestrial Radio Access Network (E-UTRAN).

At least some aspects of the systems and methods disclosed herein may bedescribed in relation to the 3GPP LTE, LTE-Advanced (LTE-A) and otherstandards (e.g., 3GPP Releases 8, 9, 10, 11 and/or 12). However, thescope of the present disclosure should not be limited in this regard. Atleast some aspects of the systems and methods disclosed herein may beutilized in other types of wireless communication systems.

A wireless communication device may be an electronic device used tocommunicate voice and/or data to a base station, which in turn maycommunicate with a network of devices (e.g., public switched telephonenetwork (PSTN), the Internet, etc.). In describing systems and methodsherein, a wireless communication device may alternatively be referred toas a mobile station, a UE, an access terminal, a subscriber station, amobile terminal, a remote station, a user terminal, a terminal, asubscriber unit, a mobile device, etc. Examples of wirelesscommunication devices include cellular phones, smart phones, personaldigital assistants (PDAs), laptop computers, netbooks, e-readers,wireless modems, etc. In 3GPP specifications, a wireless communicationdevice is typically referred to as a UE. However, as the scope of thepresent disclosure should not be limited to the 3GPP standards, theterms “UE” and “wireless communication device” may be usedinterchangeably herein to mean the more general term “wirelesscommunication device.” A UE may also be more generally referred to as aterminal device.

In 3GPP specifications, a base station is typically referred to as aNode B, an evolved Node B (eNB), a home enhanced or evolved Node B(HeNB) or some other similar terminology. As the scope of the disclosureshould not be limited to 3GPP standards, the terms “base station,” “NodeB,” “eNB,” and “HeNB” may be used interchangeably herein to mean themore general term “base station.” Furthermore, the term “base station”may be used to denote an access point. An access point may be anelectronic device that provides access to a network (e.g., Local AreaNetwork (LAN), the Internet, etc.) for wireless communication devices.The term “communication device” may be used to denote both a wirelesscommunication device and/or a base station. An eNB may also be moregenerally referred to as a base station device.

It should be noted that as used herein, a “cell” may refer to any set ofcommunication channels over which the protocols for communicationbetween a UE and eNB that may be specified by standardization orgoverned by regulatory bodies to be used for International MobileTelecommunications-Advanced (IMT-Advanced) or its extensions and all ofit or a subset of it may be adopted by 3GPP as licensed bands (e.g.,frequency bands) to be used for communication between an eNB and a UE.“Configured cells” are those cells of which the UE is aware and isallowed by an eNB to transmit or receive information. “Configuredcell(s)” may be serving cell(s). The UE may receive system informationand perform the required measurements on all configured cells.“Activated cells” are those configured cells on which the UE istransmitting and receiving. That is, activated cells are those cells forwhich the UE monitors the physical downlink control channel (PDCCH) andin the case of a downlink transmission, those cells for which the UEdecodes a physical downlink shared channel (PDSCH). “Deactivated cells”are those configured cells that the UE is not monitoring thetransmission PDCCH. It should be noted that a “cell” may be described interms of differing dimensions. For example, a “cell” may have temporal,spatial (e.g., geographical) and frequency characteristics.

The systems and methods disclosed may involve carrier aggregation.Carrier aggregation refers to the concurrent utilization of more thanone carrier. In carrier aggregation, more than one cell may beaggregated to a UE. In one example, carrier aggregation may be used toincrease the effective bandwidth available to a UE.

It should be noted that the term “concurrent” and variations thereof asused herein may denote that two or more events may overlap each other intime and/or may occur near in time to each other. Additionally,“concurrent” and variations thereof may or may not mean that two or moreevents occur at precisely the same time.

Licensed-assisted access (LAA) may support LTE in unlicensed spectrum.In a LAA network, the downlink (DL) transmission may be scheduled in anopportunistic manner. Thus, listen before talk (LBT) with clear channelassessment (CCA) may be performed before a LAA transmission.Additionally, backoff algorithms may be employed to reduce the collisionprobability of a LAA transmission with other unlicensed signals.

The backoff algorithms may be applied on each LAA serving cell or LAAtransmitting node. However, the contention mechanisms of backoffprocedures try to avoid simultaneous transmissions from different LAAcells. This may be desirable for WiFi-based transmission because allpackets have the same header structure. On the other hand, simultaneoussubframe transmissions in LTE (e.g., with coordinated multipoint (CoMP)transmission) may be beneficial to improve the overall system throughputand increase spectrum efficiency.

Systems and methods for managed simultaneous LAA transmissions whenmultiple LAA serving cells share the same unlicensed carrier and arecontrolled by the same eNB scheduler are described herein. Additionally,systems and methods are described to avoid undesirable simultaneoustransmissions from multiple LAA cells. Furthermore, systems and methodsare described to avoid a hidden terminal issue among cells that aremanaged by the same eNB or the same operator. The described systems andmethods may be achieved by a coordinated management of backoff countersamong LAA cells managed by the same eNB or operator.

In one approach, one or more LAA cells may have backoff counters aszero. Restrictions on the backoff counter set to zero may be applied toprovide fairness among the LAA cells.

In another approach, a relaxed defer transmission behavior may be used.The backoff counter handling may be extended into other values when thebackoff counter is not zero, including group LAA cell alignment.Behaviors when the backoff counter is modified in these cases aredefined herein. Also, to ensure fairness among LAA cells, someconstraints may be applied for backoff counter handling.

Various examples of the systems and methods disclosed herein are nowdescribed with reference to the Figures, where like reference numbersmay indicate functionally similar elements. The systems and methods asgenerally described and illustrated in the Figures herein could bearranged and designed in a wide variety of different implementations.Thus, the following more detailed description of severalimplementations, as represented in the Figures, is not intended to limitscope, as claimed, but is merely representative of the systems andmethods.

FIG. 1 is a block diagram illustrating one implementation of one or moreeNBs 160 and one or more UEs 102 in which systems and methods for LAAmay be implemented. The one or more UEs 102 communicate with one or moreeNBs 160 using one or more antennas 122 a-n. For example, a UE 102transmits electromagnetic signals to the eNB 160 and receiveselectromagnetic signals from the eNB 160 using the one or more antennas122 a-n. The eNB 160 communicates with the UE 102 using one or moreantennas 180 a-n.

The UE 102 and the eNB 160 may use one or more channels 119, 121 tocommunicate with each other. For example, a UE 102 may transmitinformation or data to the eNB 160 using one or more uplink channels121. Examples of uplink channels 121 include a PUCCH and a PUSCH, etc.The one or more eNBs 160 may also transmit information or data to theone or more UEs 102 using one or more downlink channels 119, forinstance. Examples of downlink channels 119 include a PDCCH, a PDSCH,etc. Other kinds of channels may be used.

Each of the one or more UEs 102 may include one or more transceivers118, one or more demodulators 114, one or more decoders 108, one or moreencoders 150, one or more modulators 154, a data buffer 104 and a UEoperations module 124. For example, one or more reception and/ortransmission paths may be implemented in the UE 102. For convenience,only a single transceiver 118, decoder 108, demodulator 114, encoder 150and modulator 154 are illustrated in the UE 102, though multipleparallel elements (e.g., transceivers 118, decoders 108, demodulators114, encoders 150 and modulators 154) may be implemented.

The transceiver 118 may include one or more receivers 120 and one ormore transmitters 158. The one or more receivers 120 may receive signalsfrom the eNB 160 using one or more antennas 122 a-n. For example, thereceiver 120 may receive and downconvert signals to produce one or morereceived signals 116. The one or more received signals 116 may beprovided to a demodulator 114. The one or more transmitters 158 maytransmit signals to the eNB 160 using one or more antennas 122 a-n. Forexample, the one or more transmitters 158 may upconvert and transmit oneor more modulated signals 156.

The demodulator 114 may demodulate the one or more received signals 116to produce one or more demodulated signals 112. The one or moredemodulated signals 112 may be provided to the decoder 108. The UE 102may use the decoder 108 to decode signals. The decoder 108 may produceone or more decoded signals 106, 110. For example, a first UE-decodedsignal 106 may comprise received payload data, which may be stored in adata buffer 104. A second UE-decoded signal 110 may comprise overheaddata and/or control data. For example, the second UE-decoded signal 110may provide data that may be used by the UE operations module 124 toperform one or more operations.

As used herein, the term “module” may mean that a particular element orcomponent may be implemented in hardware, software or a combination ofhardware and software. However, it should be noted that any elementdenoted as a “module” herein may alternatively be implemented inhardware. For example, the UE operations module 124 may be implementedin hardware, software or a combination of both.

In general, the UE operations module 124 may enable the UE 102 tocommunicate with the one or more eNBs 160. The UE operations module 124may provide information 148 to the one or more receivers 120. Forexample, the UE operations module 124 may inform the receiver(s) 120when to receive retransmissions.

The UE operations module 124 may provide information 138 to thedemodulator 114. For example, the UE operations module 124 may informthe demodulator 114 of a modulation pattern anticipated fortransmissions from the eNB 160.

The UE operations module 124 may provide information 136 to the decoder108. For example, the UE operations module 124 may inform the decoder108 of an anticipated encoding for transmissions from the eNB 160.

The UE operations module 124 may provide information 142 to the encoder150. The information 142 may include data to be encoded and/orinstructions for encoding. For example, the UE operations module 124 mayinstruct the encoder 150 to encode transmission data 146 and/or otherinformation 142. The other information 142 may include PDSCH HARQ-ACKinformation.

The encoder 150 may encode transmission data 146 and/or otherinformation 142 provided by the UE operations module 124. For example,encoding the data 146 and/or other information 142 may involve errordetection and/or correction coding, mapping data to space, time and/orfrequency resources for transmission, multiplexing, etc. The encoder 150may provide encoded data 152 to the modulator 154.

The UE operations module 124 may provide information 144 to themodulator 154. For example, the UE operations module 124 may inform themodulator 154 of a modulation type (e.g., constellation mapping) to beused for transmissions to the eNB 160. The modulator 154 may modulatethe encoded data 152 to provide one or more modulated signals 156 to theone or more transmitters 158.

The UE operations module 124 may provide information 140 to the one ormore transmitters 158. This information 140 may include instructions forthe one or more transmitters 158. For example, the UE operations module124 may instruct the one or more transmitters 158 when to transmit asignal to the eNB 160. For instance, the one or more transmitters 158may transmit during a UL subframe. The one or more transmitters 158 mayupconvert and transmit the modulated signal(s) 156 to one or more eNBs160.

The eNB 160 may include one or more transceivers 176, one or moredemodulators 172, one or more decoders 166, one or more encoders 109,one or more modulators 113, a data buffer 162 and an eNB operationsmodule 182. For example, one or more reception and/or transmission pathsmay be implemented in an eNB 160. For convenience, only a singletransceiver 176, decoder 166, demodulator 172, encoder 109 and modulator113 are illustrated in the eNB 160, though multiple parallel elements(e.g., transceivers 176, decoders 166, demodulators 172, encoders 109and modulators 113) may be implemented.

The transceiver 176 may include one or more receivers 178 and one ormore transmitters 117. The one or more receivers 178 may receive signalsfrom the UE 102 using one or more antennas 180 a-n. For example, thereceiver 178 may receive and downconvert signals to produce one or morereceived signals 174. The one or more received signals 174 may beprovided to a demodulator 172. The one or more transmitters 117 maytransmit signals to the UE 102 using one or more antennas 180 a-n. Forexample, the one or more transmitters 117 may upconvert and transmit oneor more modulated signals 115.

The demodulator 172 may demodulate the one or more received signals 174to produce one or more demodulated signals 170. The one or moredemodulated signals 170 may be provided to the decoder 166. The eNB 160may use the decoder 166 to decode signals. The decoder 166 may produceone or more decoded signals 164, 168. For example, a first eNB-decodedsignal 164 may comprise received payload data, which may be stored in adata buffer 162. A second eNB-decoded signal 168 may comprise overheaddata and/or control data. For example, the second eNB-decoded signal 168may provide data (e.g., PDSCH HARQ-ACK information) that may be used bythe eNB operations module 182 to perform one or more operations.

In general, the eNB operations module 182 may enable the eNB 160 tocommunicate with the one or more UEs 102. The eNB operations module 182may include one or more of a multiple LAA cell coordination module 194and a hidden terminal avoidance module 196.

For unlicensed spectrum, contention access mechanisms are required sothat the unlicensed devices can have some fair access. Typically,listen-before-talk (LBT) may be performed. If the channel is sensed asbusy, an unlicensed device should defer the transmission and contend foraccess when the channel is idle again. If two or more unlicensed devicescapture the same channel at the same time, a collision occurs. Thepackets may not be received correctly due to the collision andinterference from other packets. Thus, a multiple access channel may betreated as a single channel with exclusive usage by a single unlicenseddevice.

This approach is good for WiFi-type asynchronous transmissions. But forLTE, coordinated multi-point (CoMP) transmission is supported. The CoMPtransmission may include joint processing or coordinated scheduling.Simultaneous transmissions from adjacent transmit points or cells can beused to improve the overall system throughput and spectrum efficiency.

If scheduled wisely, simultaneous LAA transmissions from adjacent LAAcells on the same carrier may be considered. On the other hand, sinceLAA is a scheduled transmission by a scheduler, the scheduler may avoida collision if multiple LAA nodes get the channel at the same time andsimultaneous transmission is not desirable.

As used herein, the term LAA cell refers to a set of communicationchannels between a UE 102 and an eNB 160 in which LAA operations may beperformed. A LAA cell refers to a serving cell that operates on anunlicensed carrier. In current definition, a LAA cell can only be asecondary cell, and is configured by a licensed cell. An LAA cell mayalso be referred to as an LAA serving cell.

Additionally, a hidden terminal issue exists if the transmitter cannotsense another transmission close to the receiver. An example of thehidden terminal issue is described in connection with FIG. 5 below.

LAA extends LTE transmission on unlicensed band. Unlike 802.11 where thesame preamble sequence and header format/modulation is used by allstations, a LTE signal is scrambled with information including a cellidentity and scrambling sequences. Thus, the LTE signal is more robustwith interference mitigation techniques. A collision with another LTEsignal may cause some degradation of a LTE signal and should be avoided.On the other hand, in some cases, simultaneous LTE transmission may bebeneficial to the overall throughput or spectrum efficiency. Someexamples of simultaneous LTE transmission are discussed in FIG. 6.

To avoid the hidden terminal problem and undesirable collisions, and totake advantage of simultaneous LTE transmissions for LAA, detailedsolutions on channel access and backoff mechanisms may defined asdescribed herein.

In one implementation, multiple LAA cell operation may be defined. In atypical LAA small cell scenario, a common scheduler schedules one ormore licensed cells and one or more LAA small cells under each licensedcell. The deployment of LAA small cells is managed by operators.Multiple LAA cells in an area may be controlled by the same scheduler(e.g., by the same eNB 160) or managed by the same operator.

In licensed small cell scenarios, the LTE cell DL transmission is alwayspresent in each cell. Thus, interference from adjacent cells can be veryserious. CoMP methods can be used to improve the cell-edge UE 102throughputs by joint processing. For example, joint processing mayinclude transmitting the same signal from multiple points.Alternatively, coordinated scheduling and coordinated beamforming(CS/CB) may be used so that the interference from adjacent cells to a UE102 is minimized. Furthermore, inter-cell interference coordination(ICIC) methods may be employed to mitigate the problem. For example, analmost blank subframe may be used in an adjacent cell.

With license-assisted access on an unlicensed carrier, a LAA cell cannottransmit all the time. A LAA transmission should occur if it has data tobe transmitted and if the channel is not occupied by other unlicensedtransmissions. Therefore, a LAA signal should have less interferencefrom adjacent LAA cells. Moreover, joint processing and CS/CB frommultiple LAA cells can further enhance the system throughput andspectrum efficiency.

In one approach for LAA transmission without coordination among adjacentLAA cells, in each LAA cell, listen before talk (LBT) with clear channelassessment (CCA) is required before a LAA transmission. To reduce thecollision probability, some backoff mechanisms are needed. Thus, thebackoff mechanisms are performed independently in each LAA node.

If a LAA node (e.g., eNB 160) has data to transmit, the LAA node mayperform CCA detection and a contention access mechanism. It should benoted that the detailed backoff mechanisms and the CCA timeslot sizesmay be performed according to known approaches.

A LAA node may acquire the channel and start to transmit LAA subframesif the LAA node sensed a CCA timeslot as idle and the backoff counterreaches 0. If one LAA node obtains the channel and starts transmission,the other adjacent LAA nodes sense the channel as busy and will nottransmit.

Collision or simultaneous LAA transmissions may occur only if more thanone LAA transmit points get channel access at the same LAA CCA timeslot.A simplified flowchart for a LAA cell is described in connection withFIG. 7.

If no multiple LAA cooperation is applied, there may be two potentialissues. In a first case, the LAA transmission may become exclusive. Inthis case, simultaneous LAA transmission from multiple LAA cells cannotbe scheduled even if it is desirable. In a second case, if multiple LAAcells obtain the channel at the same time, simultaneous LAAtransmissions may occur even if it is not desirable and causescollision. It should be noted that to obtain the channel by a LAA cellmeans that the eNB 160 is allowed to transmit a downlink signalimmediately on the given LAA cell. However, the scheduler may determinenot to transmit on the LAA cell.

The multiple LAA cell coordination module 194 may perform coordinatedLAA backoff with simultaneous LAA transmissions. For LAA eNBs 160 underthe same scheduler (i.e., under the same eNB 160 or managed by the sameoperator), the scheduler may have knowledge of the adjacent cells ofeach LAA node, the CCA detection result and the backoff counter of eachLAA node. The feedback information can be used to achieve differentfunctions. For example, the feedback information may be used for hiddenterminal avoidance and CoMP transmissions. The available feedbackinformation can be used for cooperative multiple LAA cell operations.

The approaches disclosed herein can be achieved by managing backoffcounters at each LAA cell. It should be noted that the approachesdisclosed herein are independent of the backoff algorithms and the CCAslot sizes used. Furthermore, the approaches disclosed herein may beemployed independently or jointly with each other.

In a first approach, the multiple LAA cell coordination 194 may performa coordinated LAA backoff with simultaneous LAA transmissions. Withcoordinated operation, the scheduler maintains a list of LAA cells ortransmit points (TP) in an area. The scheduler may also know therelative location of each LAA cell. For example, for each LAA cell, thescheduler may have a list of adjacent LAA cells of the given LAA cellthat operate on the same unlicensed carrier. Furthermore, the schedulermay know the CCA detection result and the backoff counter of each LAAnode.

For each LAA cell or TP, listen before talk (LBT) with clear channelassessment (CCA) is required before a LAA transmission. The backoffmechanisms are also performed independently in each LAA node. If a LAAnode has data to transmit, it may perform CCA detection and a contentionaccess mechanism. A LAA node may obtain the channel and transmit LAAsubframes if it senses a CCA timeslot as idle and the backoff counterreaches 0. The coordinated operation may be performed if at least one ofthe LAA nodes managed by the same scheduler obtains the channel.

There are several cases to be considered. In a first case, only one LAAnode/cell/TP obtains the channel in a CCA timeslot. This case isdescribed in more detail in connection with FIG. 8. In a second case,multiple LAA cells obtain the channel at the same CCA timeslot. Thiscase is described in more detail in connection with FIG. 9.

In a second approach, the hidden terminal avoidance module 196 mayperform coordinated LAA procedures with hidden terminal avoidance andcollision avoidance. As described above, the hidden terminal issueexists in contention access networks. In WiFi, a request to send(RTS)/clear to send (CTS) message exchange is used to preempt thechannel. In LAA, such a mechanism may be difficult to implement,especially for downlink (DL)-only LAA transmissions.

In LAA, the UL feedback of instantaneous channel condition from the UE102 side is not possible. However, for LAA eNBs 160 under the samescheduler (i.e., under the same eNB 160 or managed by the sameoperator), the scheduler may have the information of the adjacent cellsof each LAA node. For example, the scheduler may have the CCA detectionresults and the backoff counter of the adjacent cells of each LAA node.Thus, both coordinated multi-point (CoMP) transmission operations andhidden node issues can be solved by managing the backoff counters at theLAA nodes under the same scheduler.

For LAA nodes under the same scheduler, the eNB 160 can obtain theadjacent LAA cell information for each LAA node by either LAA celldetection or operator deployment. Each LAA node may maintain its own CCAand LBT operation, and each LAA node may manage its own backoff counter,which is known to the common scheduler. This approach is described inmore detail in connection with FIG. 10.

With coordinated LAA cells operation, the functions for simultaneoustransmission and hidden terminal avoidance can be applied jointly orindependently at the scheduler. These functions can be achieved with thefollowing benefits. Desirable simultaneous LAA transmissions (e.g.,CoMP-like schemes) from multiple LAA cells may be performed. Undesirablesimultaneous LAA transmissions when multiple LAA cells obtain thechannel in the same timeslot may be avoided. Hidden terminals may beavoided by using CCA detection feedback of adjacent cells.

A general description of channel access and backoff procedure isdescribed in connection with FIG. 11. In an example, the LAA cell may beconfigured with an initial CW size or minimum CW size X=CW0, and amaximum CW size Y=CWmax. A backoff process may be required after theinitial LAA transmission (as shown in FIG. 11 for continuous LAAtransmissions) or for a subframe re-transmission. For dynamic CWadjustment, the CW size may be initiated with CW0, and increased to thenext CW size (e.g., double the previous CW size), if a collision isobserved, until CWmax is reached.

As described herein, setting the backoff counter to zero may allowimmediate transmission from the given LAA cell. This effectivelyprovides better access probability to the given LAA cell since it doesnot contend the channel by itself. To ensure the fairness of contentionamong LAA cells, some constraints may be applied to simultaneoustransmission by setting the backoff counter to zero.

In one approach, simultaneous immediate transmission is only allowedfrom LAA cells with backoff counters that are smaller than or equal to athreshold value (e.g., 4, 5, 8, 10, 16, etc.). The threshold value maybe a fixed value or may be configured by higher layer signaling.

In another approach, simultaneous immediate transmission is only allowedfrom the LAA cells with the minimum or initial contention window size(CWS). In another approach, simultaneous immediate transmission is onlyallowed from the LAA cells with the same contention window size (CWS) asthe LAA cell with a backoff counter that reaches 0. In yet anotherapproach, simultaneous immediate transmission is only allowed from theLAA cells with the same or smaller contention window size (CWS) as theLAA cell with a backoff counter that reaches 0.

One of the reasons to defer transmission is to allow frequency reuse andsimultaneous LAA transmissions from multiple LAA cells. However, thedeferring of an initial CCA (ICCA) may bring a loop for the LAA cell todefer with a larger CCA slot size. It is difficult to align thetransmission of another LAA cell following the ICCA slot boundaries.Examples of issues with ICCA deferring after the backoff count reacheszero are discussed in connection with FIG. 12.

Therefore, to enable frequency reuse, some enhancements may be employedfor the zero counter deferring transmission. In a first approach, if theCCA slots are synchronized among LAA cells, the current initial accessbehavior for when the backoff counter reaches zero and when the LAA celldetermines not to transmit can be enhanced by replacing the ICCA idlesensing time with an ECCA idle sensing time.

This first approach allows the eNB 160 to wait for any number of ECCAslots to align with the transmission of another LAA cell when it reaches0. It should be noted that if in any CCA slot when the LAA cell isdeferring the transmission, if the channel is sensed busy, a backoffprocess is initiated by randomly generating a backoff counter among 0and contention window size (CWS) −1. The LAA cell has to wait for thechannel to be idle for a defer period before the backoff counter countsdown.

In a second approach, the deferring time of a LAA cell can be moreflexible. When the backoff counter of a LAA cell reaches 0, it has theopportunity to transmit a LAA TxOP. If the LAA cell gives up immediatetransmission, it can still hold the opportunity for a given period, asshown in FIG. 13 below. In this approach, the LAA cell can transmit atany given time within a zero counter defer period. This approach workseven if the CCA slots of a different LAA cell are not synchronized.Also, it is applicable if the ICCA length, defer period length and ECCAlength are not aligned with each other.

Backoff counter alignment among LAA cells may be defined according tothe systems and methods described herein. In one approach, the backoffcounter and transmission alignment can be performed before the backoffcounter reaches zero to facilitate frequency reuse. With an alignedbackoff counter (especially when the backoff counter value is small),there is a better chance to have simultaneous transmission from some LAAcells in the group of cells configured for frequency reuse.

In one implementation of backoff counter alignment, a single backoffcounter is shared among the group of LAA cells. Thus, the CCA slots maybe synchronized among these cells. The channel status may be determinedbased on the channel sensing results of all LAA cells included in thegroup. The channel may be viewed as busy if any of the LAA cell in thegroup senses the channel as busy. The channel may be viewed as idle ifall of the LAA cells in the group sense the channel as idle.

In another approach, the backoff counter alignment may be performedamong LAA cells for frequency reuse. The backoff counter alignment maybe performed periodically or triggered by higher layer signaling. In abackoff counter alignment, the backoff counters of the LAA cells may bereset with the same value.

With backoff counter alignment, the backoff counter of a given LAA cellmay be increased, decreased or maintained the same. Therefore, a LAAcell will get better channel access probability if it has a very largebackoff counter value and the backoff counter is decreased to a verysmall value. On the other hand, a LAA cell will get worse channel accessprobability if it has a very small backoff counter value and the backoffcounter is increased to a very large value. To preserve contentionfairness among LAA cells, some limitations may be applied for the LAAcells performing backoff counter alignment.

In a first approach to backoff counter alignment (i.e., approach 1), thebackoff counter alignment can only be performed within LAA cells with abackoff counter smaller than a threshold value. The threshold value canbe a fixed value (e.g., 5, 8, 10, 16, etc.). The threshold can beconfigured as the minimum or initial contention window size (CWS) orhalf of the initial CWS. The threshold value may be configured by higherlayer signaling.

In a second approach to backoff counter alignment (i.e., approach 2),the backoff counter alignment can only be performed within LAA cellswith the difference of counter values within a given range. In otherwords, assume the maximum backoff counter value is A, and the minimumbackoff counter in the LAA cells for backoff counter alignment is B. Thevalue of (A-B) should be smaller than a threshold value. The thresholdvalue can be a fixed value (e.g., 5, 8, 10, 16, etc.). The threshold canbe configured as the minimum or initial contention window size (CWS) orhalf of the initial CWS. The threshold value may be configured by higherlayer signaling.

In a third approach to backoff counter alignment (i.e., approach 3), thebackoff counter alignment can only be performed within LAA cells withthe same contention window size (CWS). The LAA cells with the same CWSexperience similar collision situations and are at the same contentionstage.

In a fourth approach to backoff counter alignment (i.e., approach 4),the backoff counter alignment can only be performed within LAA cellsthat sense the channel in idle state and in a backoff counter count downprocess. Thus, for a LAA with a backoff counter frozen or suspended dueto the channel sensed as busy or in a defer period, backoff counteralignment with other LAA cells cannot be applied. This fourth approachmay be combined together with approaches 1-3 above for backoff counteralignment.

Since frequency reuse is achieved by simultaneous transmissions ofmultiple LAA cells on the same carrier, it has benefits of higheroverall throughput and less resource usage than exclusive transmissionsof multiple LAAs. There are two other issues for backoff counteralignment. The first issue is determining what backoff counter valueshould be set after the backoff counter alignment. The second issue isdetermining the LAA cell behavior after the backoff counter change withalignment.

For the first issue, after a backoff counter alignment, the same valuecan be set to the LAA cells performing backoff counter alignment.Several approaches may be used to determine the aligned backoff counteramong the LAA cells for backoff counter alignment.

In one approach, the average or mean backoff counter value among thegroup of LAA cells is used to align the backoff counters. The alignedbackoff counter value can be the rounded integer value of the average ormean value of all backoff counters of the LAA cells for backoff counteralignment. The aligned backoff counter value can be the integer value ofa floor or ceiling function of the average or mean value of all backoffcounters of the LAA cells for backoff counter alignment.

In another approach, the minimum backoff counter value among the groupof LAA cells is used to align the backoff counters. Thus, the LAA cellswith larger backoff counters will be decreased to the same as the LAAcell with the minimum backoff counter in the LAA cells for backoffcounter alignment.

In yet another approach, the maximum backoff counter value among thegroup of LAA cells is used to align the backoff counters. Thus, the LAAcells with smaller backoff counters will be increased to the same as theLAA cell with the maximum backoff counter in the LAA cells for backoffcounter alignment.

For the second issue, two approaches may be considered for the LAA cellbehavior after the backoff counter change with backoff counteralignment. In one approach, after the backoff counter alignment, a LAAcell has to wait for an idle period of a defer period or an ICCA timebefore the backoff counter counts down resumes. This provides aconsistent behavior for all LAA cells regardless the previous channelstates when the backoff counter alignment is performed. Therefore, thisapproach works even if approach 4 above is not applied. This approachcan force a resynchronization of all participating LAA cells on the CCAslot structure.

In another approach, after the backoff counter alignment, a LAA cellperforms normal count down. In other words, if a LAA cell is in countdown and senses the channel is idle for an ECCA slot, the backoffcounter can count down without waiting for an idle period of a deferperiod or an ICCA time before the backoff counter count down resumes.This provides a natural transition of backoff counter handling withoutinterrupting the backoff counter count down process. This approachreduces the waiting time after a backoff counter alignment, especiallyif approach 4 above is employed, where only LAA cells in a count downstate participate in the backoff counter alignment. This is becausethere is no need for an extra ICCA or defer period before count downresumes.

In the case where a LAA cell is in the state of channel busy or under abackoff counter freeze in an ICCA or a defer period, the LAA cell canperform normal count down with the newly aligned backoff counter. Thus,if the LAA cell is under a backoff counter freeze for an ICCA or deferperiod, the idle time is accumulated as normal. In another alternative,after a backoff counter alignment, the LAA cell needs to wait for a newdefer period before the backoff counter count down resumes.

Further enhancements may be implemented for backoff counter handlingbeyond a zero backoff counter. Currently, for a LAA cell, the eNB 160has several basic backoff counter handling actions. The eNB 160 mayinitiate a backoff counter within a contention window size (CWS). TheeNB 160 may suspend or freeze a backoff counter if the channel is busyor in a defer period or an ICCA period. The eNB 160 may reduce thebackoff counter by one if the channel is idle for an ECCA slot. When thebackoff counter reaches 0, the eNB 160 may transmit immediately or deferthe LAA transmission.

To better utilize benefits of frequency reuse, the eNB 160 may use amore flexible backoff counter handling to adjust the backoff counter ofa LAA cell and to align it with other LAA cells under the same eNB 160or scheduler.

Besides the basic backoff counter handling, the eNB 160 may performenhanced backoff counter handling. For example, in the channel busy ordefer period, the eNB 160 may allow a backoff counter change including abackoff counter increase or backoff counter decrease. This may be usedto align the backoff counter with one or more LAA cells under the sameeNB 160 or scheduler.

During the backoff counter count down process, even if the channel issensed idle for an ECCA, the eNB 160 may allow a backoff counter freezeor suspend. The eNB 160 may allow a backoff counter change including abackoff counter increase or backoff counter decrease.

To provide some fairness among LAA cells and other unlicensedtransmissions, some constrains can be applied to limit the cases forbackoff counter handling. In one approach, the backoff counter changemay be limited to the current CWS of the LAA cell. The backoff countermay not be changed out of the current CWS.

In another approach, the backoff counter change is limited to a rangefrom the current backoff counter. For example, for the current backoffcounter N, a threshold k can be applied, so that the backoff counter canonly be changed between min(0, N−k) and N+k. If this restriction iscombined with the previous restriction, the backoff counter can only belimited between min(0, N−k) and min(current CWS, N+k).

In yet another approach, the backoff counter of a LAA cell may only bechanged for a limited number of times. For example, a LAA cell canperform enhanced backoff counter handling a maximum of 3 times or 5times.

For the behavior of a LAA cell after an enhanced backoff counterhandling, two approaches may be considered for the LAA cell behaviorafter the backoff counter change with backoff counter alignment. In oneapproach, after the backoff counter alignment, a LAA cell has to waitfor an idle period of a defer period or an ICCA time before the backoffcounter count down resumes. This provides a consistent behavior for allLAA cells regardless the previous channel states when the backoffcounter alignment is performed (i.e., even if approach 4 above is notapplied). This approach can force a resynchronization of allparticipating LAA cells on the CCA slot structure.

In another approach, after the backoff counter alignment, a LAA cellperforms normal count down. In other words, if a LAA cell is in countdown and senses the channel is idle for an ECCA slot, the backoffcounter can count down without waiting for an idle period of a deferperiod or an ICCA time before the backoff counter count down resumes.This provides a natural transition of backoff counter handling withoutinterrupting the backoff counter count down process. This approachreduces the waiting time after a backoff counter alignment, especiallyif approach 4 above is employed, where only LAA cells in a count downstate participate in the backoff counter alignment. This is becausethere is no need for an extra ICCA or defer period before count downresumes.

In the case where a LAA cell is in the state of channel busy or under abackoff counter freeze in an ICCA or a defer period, the LAA cell canperform normal count down with the newly aligned backoff counter. Thus,if the LAA is under a backoff counter freeze for an ICCA or deferperiod, the idle time is accumulated as normal. In another alternative,after a backoff counter alignment, the LAA cell needs to wait for a newdefer period before the backoff counter count down resumes.

The eNB operations module 182 may provide information 188 to thedemodulator 172. For example, the eNB operations module 182 may informthe demodulator 172 of a modulation pattern anticipated fortransmissions from the UE(s) 102.

The eNB operations module 182 may provide information 186 to the decoder166. For example, the eNB operations module 182 may inform the decoder166 of an anticipated encoding for transmissions from the UE(s) 102.

The eNB operations module 182 may provide information 101 to the encoder109. The information 101 may include data to be encoded and/orinstructions for encoding. For example, the eNB operations module 182may instruct the encoder 109 to encode transmission data 105 and/orother information 101.

The encoder 109 may encode transmission data 105 and/or otherinformation 101 provided by the eNB operations module 182. For example,encoding the data 105 and/or other information 101 may involve errordetection and/or correction coding, mapping data to space, time and/orfrequency resources for transmission, multiplexing, etc. The encoder 109may provide encoded data 111 to the modulator 113. The transmission data105 may include network data to be relayed to the UE 102.

The eNB operations module 182 may provide information 103 to themodulator 113. This information 103 may include instructions for themodulator 113. For example, the eNB operations module 182 may inform themodulator 113 of a modulation type (e.g., constellation mapping) to beused for transmissions to the UE(s) 102. The modulator 113 may modulatethe encoded data 111 to provide one or more modulated signals 115 to theone or more transmitters 117.

The eNB operations module 182 may provide information 192 to the one ormore transmitters 117. This information 192 may include instructions forthe one or more transmitters 117. For example, the eNB operations module182 may instruct the one or more transmitters 117 when to (or when notto) transmit a signal to the UE(s) 102. The one or more transmitters 117may upconvert and transmit the modulated signal(s) 115 to one or moreUEs 102.

It should be noted that a DL subframe may be transmitted from the eNB160 to one or more UEs 102 and that a UL subframe may be transmittedfrom one or more UEs 102 to the eNB 160. Furthermore, both the eNB 160and the one or more UEs 102 may transmit data in a standard specialsubframe.

It should also be noted that one or more of the elements or partsthereof included in the eNB(s) 160 and UE(s) 102 may be implemented inhardware. For example, one or more of these elements or parts thereofmay be implemented as a chip, circuitry or hardware components, etc. Itshould also be noted that one or more of the functions or methodsdescribed herein may be implemented in and/or performed using hardware.For example, one or more of the methods described herein may beimplemented in and/or realized using a chipset, an application-specificintegrated circuit (ASIC), a large-scale integrated circuit (LSI) orintegrated circuit, etc.

FIG. 2 is a flow diagram illustrating a method 200 for schedulingmultiple Licensed-Assisted Access (LAA) cells by an eNB 160. The eNB 160may perform 202 CCA detection and obtain the channel status at multipleconfigured LAA cells. For example, the eNB 160 may determine whether thechannel is busy in a CCA timeslot for a given LAA cell. If the LAA cellis transmitting or the CCA detects another transmission on the same LAAcarrier, then the channel is determined to be busy. The eNB 160 maydetermine that the channel is idle in a CCA timeslot for the given LAAcell if the CCA detects no transmission on the same LAA carrier.

The eNB 160 may perform 204 channel access and backoff procedures atmultiple configured LAA cells. For example, the eNB 160 may determine abackoff counter value of a given LAA cell based on the CCA detectionresult of the given LAA cell.

The eNB 160 may determine 206 that channel access is obtained by atleast one LAA cell. For example, the eNB 160 may determine that a firstLAA cell obtains the channel if the first LAA cell detects the channelas idle in the CCA timeslot and its backoff counter reaches 0. The eNB160 may determine whether there are other LAA cells that obtain thechannel in the same timeslot.

The eNB 160 may determine 208 whether to perform or suspend downlinktransmission in one or more LAA cells based on the CCA detectionresults. For example, the eNB 160 may determine a first LAA cell for LAAtransmission. The eNB 160 may then determine if simultaneous LAAtransmissions from other LAA cells on the same carrier are desirable orbeneficial. The eNB 160 may determine whether to suspend transmission orstart LAA transmission from another LAA node.

If simultaneous LAA transmission from one or more LAA cells on the samecarrier is desirable or beneficial, then the eNB 160 may set the backoffcounter of the given LAA cell to zero. The eNB 160 may also schedule LAAtransmission from the given LAA cell. The eNB 160 may further performsimultaneous transmission on the LAA cells that are determined for LAAtransmissions. It should be noted that the same eNB 160 that schedulesthe transmission may perform simultaneous transmission on the LAA cells.Multiple LAA cell operation may be under the control of the sameoperator and same scheduler (an eNB 160 or eNBs 160 with ideal backhaulbetween each other).

If simultaneous LAA transmission from one or more LAA cells on the samecarrier is not desirable or not beneficial, then the eNB 160 may performa backoff procedure on a given adjacent cell of the first LAA cell.

If simultaneous LAA transmission from one or more given LAA cells thatobtain the channel in the same timeslot as the first LAA cell is notdesirable or not beneficial, then the eNB 160 may suspend transmissionfrom the given LAA cells. The eNB 160 may also start a new backoffprocedure on the given LAA cells. The eNB 160 may also performtransmission on other LAA cells that are determined for LAAtransmissions.

When determining that channel access is obtained by the first LAA cell,the eNB 160 may also determine adjacent LAA cells on the same carrier asthe first LAA cell based on location information of LAA cells or thefeedback of each configured LAA cell. The eNB 160 may determine whetherthere is a hidden terminal near the first LAA cell that obtains thechannel.

If any of the adjacent LAA cells of the first LAA cell detects thechannel as busy, then the eNB 160 may determine that there is a hiddenterminal near the first LAA cell that obtains the channel. The eNB 160may suspend the transmission from the first LAA cell. The eNB 160 maystart a new backoff procedure on the first LAA cell.

If all of the adjacent LAA cells of the first LAA cell detect thechannel as clear or idle, then the eNB 160 may determine that there isno hidden terminal near the first LAA cell that obtains the channel. TheeNB 160 may transmit LAA subframes on the first LAA cell.

FIG. 3 illustrates an example of a LAA subframe burst transmission. Thistransmission may also be referred to as a LAA subframe set transmission.To provide fairness to other networks on the same unlicensed carrier,the eNB 160 may configure a maximum number of continuous subframetransmissions k in a LAA cell (e.g., a set of LAA subframes or a burstof LAA subframes 339). The maximum transmission time in an unlicensedcarrier may be different in different regions and/or countries based onthe regulatory requirements.

In this example, the subframe is configured with normal cyclic prefix.The first two OFDM symbol lengths are reserved for carrier sensing.Thus, subframe 0 in a set of LAA subframes is a subframe with a reducednumber of symbols. A preamble with a partial OFDM length may betransmitted after a successful channel access in front of the first LAAsubframe with a reduced number of OFDM symbols. No sensing is necessaryfor continuous LAA subframe transmission after the first LAA subframe.The regular LTE subframe structure may be applied on consecutivesubframes in a LAA subframe set.

It should be noted that the subframe index number in FIG. 3 refers tothe index in a LAA subframe burst, instead of the subframe index in aradio frame as in legacy LTE cells.

FIG. 4 illustrates an example of LAA coexistence with other unlicensedtransmissions. A licensed serving cell 435 is shown with a 10 ms radioframe 441. A LAA serving cell 437 has LAA serving cell transmissions andother unlicensed transmissions (e.g., Wi-Fi or other LAA cells). Due tocarrier sensing and deferred transmissions, the starting of a LAAtransmission may be any subframe index in the radio frame 441 of thelicensed frame structure.

FIG. 5 illustrates an example of a hidden terminal issue with unlicensedtransmissions. The hidden terminal issue exists if a transmitter cannotsense another transmission close to the receiver. As shown in FIG. 5,the first eNB 560 a may transmit to a UE 502, but the first eNB 560 acannot hear the transmission of a second eNB 560 b. In this case, when atransmission from the first eNB 560 a starts, the transmission maycollide with another transmission from the second eNB 560 b.

In 802.11-based WiFi, a request-to-send (RTS) and clear-to-send (CTS)message exchange may be used to avoid the hidden terminal issue.However, for LAA, there is no immediate feedback from the receiverdevice (e.g., the UE 502) since LTE timing requires at least a 4 ms gapbetween a DL and UL message exchange. Thus, alleviating the hiddenterminal issue without explicit message exchange at the physical (PHY)layer is beneficial.

FIG. 6 illustrates examples of simultaneous LTE transmissions on asingle carrier. Frequency reuse and coordinated multi-point (CoMP)transmission are some examples of simultaneous LTE transmissions on asingle carrier. Different CoMP schemes may be employed to enhance theperformance.

As discussed above, the LAA extends LTE transmission on unlicensed band.Some examples of simultaneous LTE transmission are discussed in FIG. 6.In a first example (Example A), joint transmission (JT) may be usedwhere the same signal is transmitted to a single UE 602 from differenttransmit points (TPs) to improve the signal. In this first example, theTPs may include a first eNB 660 a and a second eNB 660 b that transmitthe same signal to a UE 602.

A second example (Example B) involves coordinated scheduling andcoordinated beamforming (CS/CB) where different subframes aretransmitted to different UEs 602 a-b. In this second example, a firsteNB 660 a may transmit a desired signal to a first UE 602 a. Aninterference link is also transmitted from the first eNB 660 a to asecond UE 602 b. A second eNB 660 b may transmit a desired signal to thesecond UE 602 b. An interference link is also transmitted from thesecond eNB 660 b to the first UE 602 b.

As observed in these examples, for LAA, exclusive unlicensedtransmission may be too restrictive. Therefore, coordinated simultaneoustransmission may be considered as described herein.

FIG. 7 is a flow diagram illustrating a method 700 for distributed LAAcontention access without coordination among LAA cells. The method 700may be performed by an eNB 160. Collision or simultaneous LAAtransmissions may occur only if more than one LAA transmit point getschannel access at the same LAA CCA timeslot.

Upon starting 702 the method 700, the eNB 160 may determine 704 whetherthere is data to be transmitted on a LAA carrier. If there is no data tobe transmitted on the LAA carrier, the eNB 160 may wait until there isdata to be transmitted.

If there is data to transmit on a LAA carrier, the eNB 160 may perform706 CCA detection and a contention access mechanism. For unlicensedspectrum, contention access mechanisms are required so that theunlicensed devices can have some fair access. Typically,listen-before-talk (LBT) may be performed.

The eNB 160 may determine 708 whether the channel is clear and a backoffcounter reaches zero. If the channel is sensed as busy, an unlicenseddevice should defer the transmission and contend for access when thechannel is idle again. The eNB 160 may perform another CCA detection andcontention access. If the eNB 160 determines that the channel is clearand the backoff counter reaches zero, then the eNB 160 may transmit 710data on the LAA carrier.

If two or more unlicensed devices capture the same channel at the sametime, a collision occurs. The packets may not be received correctly dueto the collision and interference from other packets. If no multiple LAAcooperation is applied, there may be two potential issues. In a firstcase, the LAA transmission may become exclusive. In this case,simultaneous LAA transmission from multiple LAA cells cannot bescheduled even if it is desirable. In a second case, if multiple LAAcells obtain the channel at the same time, simultaneous LAAtransmissions may occur even if it is not desirable and causescollision. Therefore, the eNB 160 may coordinate the transmission onmultiple LAA cells as described in connection with FIGS. 8-10.

FIG. 8 is a flow diagram illustrating a method 800 for simultaneous LAAtransmissions with coordinated LAA cell operation. The method 800 may beperformed by an eNB 160. In this case, only one LAA cell obtains achannel in a CCA timeslot.

The eNB 160 may be a scheduler. As described above, in a typical LAAsmall cell scenario, a common scheduler schedules one or more licensedcells and one or more LAA small cells under each licensed cell. Thedeployment of LAA small cells is managed by operators. Multiple LAAcells in an area may be controlled by the same scheduler (e.g., by thesame eNB 160) or managed by the same operator.

For each LAA cell or transfer point (TP) (Step 802), the eNB 160 maydetermine 804 whether there is data to be transmitted on a LAA carrier.If there is no data to be transmitted on a LAA carrier, the eNB 160 maywait until there is data to be transmitted. If there is data to transmiton a LAA carrier, the eNB 160 may perform 806 CCA detection and acontention access mechanism.

For a given CCA timeslot, the eNB 160 may determine 808 whether a firstLAA cell senses the channel as clear and whether the backoff counter forthe first LAA cell reaches zero. If the channel is sensed as busy, anunlicensed device should defer the transmission and contend for accesswhen the channel is idle again. The eNB 160 may perform another CCAdetection and contention access for each LAA cell or TP.

If the eNB 160 determines that the channel is clear and the backoffcounter reaches zero for the first LAA cell, then for each LAA cell orTP, the eNB 160 may determine 810 whether the LAA cell or TP has data totransmit. The eNB 160 may also determine whether the LAA cell or TP isin the adjacent cell list of the first LAA cell.

The scheduler (e.g., eNB 160) can evaluate the adjacent LAA cells tofigure out whether simultaneous transmission from other LAA adjacentcells can enhance the overall performance. In a CCA timeslot, if thefirst LAA cell obtains the channel (i.e., the first LAA cell has data totransmit) and the first LAA cell senses the channel as idle by CCAdetection and its backoff counter reaches 0, the scheduler may scheduleimmediate LAA transmission from the first LAA cell.

Furthermore, the scheduler may check the adjacent LAA cells of the firstLAA cell. A LAA cell may be an adjacent LAA cell if it is in an adjacentcell list of a given LAA cell. For each LAA cell or TP that has data tobe transmitted and is in the adjacent cell list of the first LAA cell,the scheduler should check the CCA detection results in the given CCAtimeslot.

The eNB 160 may determine 812 whether an adjacent LAA cell detects thechannel as clear in the given CCA timeslot. If the adjacent LAA celldetects the channel as busy, the adjacent CCA cell should perform 814backoff mechanism as normal.

If the adjacent LAA cell detects the channel is idle (i.e., clear) inthe given CCA timeslot, the eNB 160 may determine 816 whether it isbeneficial to have simultaneous LAA transmissions from the givenadjacent LAA cell. In other words, the scheduler may further evaluate ifsimultaneous LAA transmission from the adjacent LAA cell is beneficialto the overall system performance. For example, the eNB 160 maydetermine whether the simultaneous LAA transmission from the adjacentLAA cell enhances throughput or spectrum efficiency.

If simultaneous transmission from the adjacent LAA cell is notbeneficial to the overall system performance, then the adjacent LAA cellmay perform 814 backoff mechanism as normal. If simultaneoustransmission from the adjacent LAA cell is beneficial to the overallsystem performance, the eNB 160 may determine 818 whether the givenadjacent LAA cell is scheduled for simultaneous LAA transmissions. Ifthe given adjacent LAA cell is not scheduled for simultaneous LAAtransmissions, then the adjacent LAA cell may perform 814 backoffmechanism as normal.

If the given adjacent LAA cell is scheduled for simultaneous LAAtransmissions, then eNB 160 (e.g., scheduler) may set 820 the backoffcounter of the given adjacent LAA cell to zero. The eNB 160 may start822 a simultaneous LAA transmission from the given adjacent LAA celltogether with the first LAA cell.

As described herein, the eNB 160 may determine which adjacent LAA celland how many adjacent LAA cells may participate in the simultaneous LAAtransmissions. The process can be viewed as a water-filling method toachieve maximum overall spectrum efficiency.

FIG. 9 is a flow diagram illustrating a method 900 for coordinatedtransmission when multiple LAA cells obtain channel access. The method900 may be performed by an eNB 160. In this case, more than one LAAcells obtain the channel at the same CCA timeslot. In other words,multiple LAA nodes may have data to transmit. The eNB 160 may be ascheduler for multiple LAA cells in an area.

For a given CCA timeslot, the eNB 160 may determine 902 that multipleLAA cells sense a channel as clear (e.g., idle) and their backoffcounters reach zero. In a LAA network without coordination, simultaneoustransmission may occur, which may provide beneficial simultaneoustransmissions (e.g., may enhance throughput or spectrum efficiency) ormay cause undesirable packet collision.

The eNB 160 may determine 904 a first LAA cell for transmission fromamong the LAA cells that obtain the channel. With coordinated operation,the scheduler knows the backoff counters of each scheduled LAA cell.Thus, if multiple LAA cells obtain the channel at the same CCA timeslot,the eNB 160 may first evaluate if simultaneous LAA transmissions fromthese LAA cells is beneficial for overall system performance. For eachLAA cell or TP that obtains the channel at the same CCA timeslot, theeNB 160 may determine 906 whether the simultaneous LAA transmissionsfrom these LAA cells provide enhanced throughput or spectrum efficiency.

If a simultaneous LAA transmission from a given LAA cell that obtainsthe channel at the same CCA timeslot is not beneficial, the eNB 160 maystart 908 a new backoff procedure for the given LAA cell. In otherwords, for a LAA cell, if it is not beneficial for overall systemperformance, the eNB 160 may ignore the contention access and start 908a new backoff procedure on the given LAA cell. For example, the eNB 160may re-initiate the backoff counter with a random number within thecontention window size. If simultaneous LAA transmission from a LAA cellis beneficial for overall system performance, the eNB 160 may schedule910 simultaneous LAA transmissions from these LAA cells.

After evaluating the LAA cells that obtain the channel at the same CCAtimeslot, the eNB 160 can further evaluate 912 the adjacent LAA cellsscheduled for transmission based on whether simultaneous LAAtransmission is beneficial to the overall spectrum efficiency. The sameevaluation method can be used as described in connection with FIG. 8above.

If a simultaneous LAA transmission from a given adjacent LAA cell is notbeneficial, then the eNB 160 may instruct the adjacent LAA cell toperform 914 a backoff mechanism as normal. If a simultaneous LAAtransmission from a given adjacent LAA cell is beneficial, then the eNB160 may schedule 916 simultaneous LAA transmissions from the givenadjacent LAA cell. The eNB 160 may then start 918 the simultaneous LAAtransmissions from all LAA cells determined for LAA transmissions.

The cooperative multiple LAA cell operation may allow simultaneous LAAtransmissions from a LAA cell even if it does not capture the channel byitself. Furthermore, the cooperative multiple LAA cell operation mayavoid undesirable simultaneous LAA transmission when multiple LAA cellsobtain the channel at the same time.

FIG. 10 is a flow diagram illustrating a method 1000 for coordinated LAAoperation with hidden terminal avoidance. The method 1000 may beperformed by an eNB 160. The eNB 160 may be a scheduler for multiple LAAcells in an area. The eNB 160 may perform coordinated LAA procedureswith hidden terminal avoidance and collision avoidance.

As described above, the hidden terminal is an important issue forunlicensed access. Normally, interactive message exchange is required toavoid collision with a transmission from a hidden terminal that is nearthe receiver that but is not known to the transmitter. The 802.11handles hidden terminal issue with a RTS/CTS message exchange. The RTSclears the channel around the transmitter, and CTS clears the channelaround the receiver.

The issue becomes more serious for LAA because of the lack of immediatefeedback. In LTE, the timing between a DL and UL is at least 4 ms, andvice versa. With LAA, the channel condition after 4 ms can be totallydifferent. Furthermore, instantaneous and continuous feedback from a LAAUE 102 may incur too much overhead and may be too costly on the licensedor unlicensed uplink.

With LAA cells in an area managed by the same scheduler, the CCAdetection results and backoff counters of each LAA node are known to thescheduler. Such information may be used to overcome hidden terminalissues for LAA without explicit physical layer message exchange.

For each LAA cell or transfer point (TP) (Step 1002), the eNB 160 maydetermine 1004 whether there is data to be transmitted on a LAA carrier.If there is no data to be transmitted on a LAA carrier, the eNB 160 maywait until there is data to be transmitted. If there is data to transmiton a LAA carrier, the eNB 160 may perform 1006 CCA detection and acontention access mechanism.

For a given CCA timeslot, the eNB 160 may determine 1008 whether a firstLAA cell senses the channel as clear and whether the backoff counter forthe first LAA cell reaches zero. If the channel is sensed as busy, anunlicensed device should defer the transmission and contend for accesswhen the channel is idle again. The eNB 160 may perform another CCAdetection and contention access for each LAA cell or TP.

If the first LAA cell, or a LAA node, obtains a LAA channel (i.e., theLAA cell senses the channel is idle in a CCA timeslot) and the backoffcounter reduces to zero, then before the LAA transmission, the eNB 160should check the CCA detection results of the given CCA timeslot and thebackoff counters in adjacent LAA cells of the first LAA cell. The eNB160 may determine 1010 if an adjacent LAA cell of the first LAA servingcell senses the channel is busy in the same CCA timeslot.

If an adjacent LAA cell of the first LAA serving cell senses the channelis busy in the same CCA timeslot, then there are ongoing transmissionsnear the given adjacent LAA cell. To avoid the hidden terminal issue,the eNB 160 may suspend 1012 the LAA transmission for the first LAA celland may perform a new backoff procedure for the first LAA cell instead.This prevents interference to an ongoing transmission close to theadjacent LAA cell that is hidden from the first LAA cell.

If there is more than one LAA cell or node that obtains the same LAAchannel in the same timeslot, then the eNB 160 may avoid undesirablecollision from multiple LAA cells. This may be accomplished as describedin connection with FIG. 9.

If the eNB 160 determines 1010 that an adjacent LAA cell of the firstLAA serving cell senses the channel is busy in the same CCA timeslot,then for each adjacent LAA cell with a backoff counter that reaches 0,the eNB 160 may determine 1014, whether it is beneficial to havesimultaneous LAA transmissions from the given adjacent LAA cell andother LAA cells determined for transmission. If it is not beneficial tohave simultaneous LAA transmissions from the given adjacent LAA cell andother LAA cells, then the eNB 160 may suspend 1016 LAA transmission onthe LAA cells that are not determined for transmission, and perform anew backoff procedure.

If a simultaneous LAA transmission from a given adjacent LAA cell isbeneficial, then the eNB 160 may schedule 1018 simultaneous LAAtransmissions from the given adjacent LAA cell. The eNB 160 may thenstart 1020 the simultaneous LAA transmissions from all LAA cellsdetermined for LAA transmissions.

In one implementation, each LAA cell maintains its own backoff processand backoff counter. The eNB 160 performs hidden terminal avoidance andcollision avoidance by managing the backoff counters of each LAA cell.In another implementation, multiple LAA cells can be grouped into a LAAcluster, and a common backoff counter is maintained for the cluster.Thus, for the LAA cluster, in a CCA timeslot, the channel is sensed asbusy if any LAA cell in the cluster senses the channel is busy. Thechannel is idle if all LAA cells in the cluster sense the channel isidle.

This method 1000 of hidden terminal avoidance does not need active UE102 feedback like in RTS/CTS. The most conservative way to implementhidden terminal avoidance is to assume that a hidden terminal exists ifany of the adjacent LAA cells detect the channel is occupied. However,as a further enhancement, the LAA scheduler (e.g., eNB 160) may evaluatethe hidden terminal problems based on the relative location of thetarget UE 102. For example, if the UE 102 is close to an adjacent LAAcell that detects the channel as busy, the scheduler should assume ahidden terminal exists and may defer LAA transmission. On the contrary,if the target UE 102 is far from an adjacent LAA cell that detects thechannel is busy, the scheduler may perform LAA transmission in the givenLAA cell.

FIG. 11 is a flow diagram illustrating a method 1100 for LAA statetransition with variable length backoff. The method 1100 may beimplemented by an eNB 160. The eNB 160 may communicate with one or moreUEs 102 in a wireless communication network. In one implementation, thewireless communication network may include an LTE network. The eNB 160may configure an unlicensed LAA cell from a licensed LTE cell. FIG. 11illustrates an example of channel access and backoff procedures that maybe performed by the eNB 160 based on a CW size determination.

The eNB may perform an initial CCA procedure. The eNB 160 may enter 1102an idle state. The eNB 160 may determine 1104 whether it needs totransmit. If the eNB 160 does not need to transmit, then the eNB 160 mayre-enter 1102 the idle state.

If the eNB 160 determines 1104 that it does need to transmit, then theeNB 160 may determine 1106 whether a channel in unlicensed spectrum(e.g., an LAA channel) is idle for an initial CCA period (BiCCA). Forexample, the eNB 160 may determine whether the channel has been idle forat least 34 microseconds (us). If the channel has been idle for theinitial CCA period, then the eNB 160 may transmit 1108. The eNB 160 maydetermine 1110 whether another transmission is needed. If notransmission is needed, the eNB 160 may re-enter 1102 the idle state.

If the eNB 160 determines 1110 that another transmission is needed orthe eNB 160 determines 1106 that the channel is not idle for the initialCCA period, then the eNB 160 may perform an extended CCA (ECCA)procedure. The eNB 160 may generate 1112 a random counter N out of [0,q−1]. In this case, the random counter N is the backoff counter. In animplementation of the backoff process, N is suspended if the channel isbusy. The LAA cell may transmit if N becomes 0.

The eNB 160 may generate 1112 the random counter using a contentionwindow (CW) size (q). The eNB 160 may update 1114 the CW between X and Yvia a dynamic exponential backoff or a semi-static backoff. X may be aminimum CW size (CW0) and Y may be a maximum CW size (CWmax). The eNB160 may update 1114 the CW size using input (e.g., ACKs/NACKs) asdescribed above in connection with FIG. 1.

Upon generating 1112 the random counter N, the eNB 160 may determine1116 whether the channel has been idle for an eCCA defer period (DeCCA).For example, the eNB 160 may determine whether the channel has been idlefor at least 34 microseconds (us). If the channel has not been idle forthe eCCA defer period, then the eNB 160 may continue to determine 1116whether the channel has been idle for an eCCA defer period.

If the eNB 160 determines 1116 that the channel has been idle for aneCCA defer period, then the eNB 160 may determine 1118 whether therandom counter N equals 0. If the random counter N equals 0, then theeNB 160 may transmit 1108. If the random counter N does not equal 0,then the eNB 160 may sense 1120 the medium for one eCCA slot duration(7). For example, the eNB 160 may sense 1120 the medium for 9 us or 10us.

Upon sensing 1120 the medium for the one eCCA slot duration, the eNB 160may determine 1122 whether the channel is busy. If the channel is busy,then the eNB 160 may wait and determine 1116 whether the channel hasbeen idle for the eCCA defer period. If the channel is not busy, thenthe eNB 160 may reduce 1124 the random counter N by 1 (e.g., N =N−1).The eNB 160 may then determine 1118 whether the random counter N equals0.

FIG. 12 illustrates examples of issues with ICCA 1243 deferring after abackoff counter reaches zero. The examples of FIG. 12 assume the channelis not occupied by any other transmission. If the backoff counter of afirst LAA cell (LAA cell-1 1237 a) reaches 0 and it chooses not totransmit, it will wait an ICCA 1243 before the next chance oftransmission.

If cell-1 1237 a and a second LAA cell (LAA cell-2 1237 b) want to waitfor each other, they will enter an infinite loop and never sync witheach other. This scenario is shown in Example (a) of FIG. 1, where thepossible transmit positions of a LAA cell 1237 defers transmission whenthe backoff counter reaches 0. Even if the channel is idle for both LAAcell-1 1237 a and LAA cell-2 1237 b, when the backoff counter of LAAcell-2 1237 bbecomes 0, LAA cell-1 1237 a cannot transmit simultaneouslywith LAA cell-2 1237 b because LAA cell-1 1237 a has to wait for an ICCA1243. This shows that the deferred transmission when the backoff counterreaches to 0 does not bring benefit to the system operation. Example (b)shows behavior after another transmission.

It should be noted that in these examples, it is assumed that the ECCA1245 and ICCA 1243 slots are fully synchronized and aligned together. Ifthe ECCA 1245 and ICCA 1243 slots are not aligned, the backoff countersynchronization and simultaneous start transmission among different LAAcells are almost impossible.

FIG. 13 illustrates an example of how an LAA cell can transmit at anygiven time within a zero counter defer period. When the backoff counterof a LAA cell reaches 0, it has the opportunity to transmit a LAA TxOP,as described above. If the LAA cell gives up immediate transmission, itcan still hold the opportunity for a given period.

The given period can be defined as a zero counter defer period. The zerocounter defer period can be defined as a length, or the length of anICCA 1243, or the length of a number of ECCA 1245 slots, where thelength or the number of slots can be a fixed value or configured byhigher layer signaling.

The LAA cell with a zero backoff counter and deferred transmission maybe allowed to transmit at any given time within the zero counter deferperiod if the channel remains as idle. The example in FIG. 13 shows thatthe backoff counter of LAA cell-2 1337 b reaches 0, and LAA cell-1 1337a can start simultaneous LAA transmissions with LAA cell-2 1337 b.

It should be noted that if in any CCA slot when the LAA cell isdeferring the transmission, if the channel is sensed busy, a backoffprocess may be initiated by randomly generating a backoff counter fromamong 0 and a contention window size (CWS)-1. The LAA cell has to waitfor the channel to be idle for a defer period before the backoff countercounts down.

FIG. 14 is a flow diagram illustrating another method 1400 forscheduling multiple Licensed-Assisted Access (LAA) cells by an eNB 160.The eNB 160 may perform 1402 CCA detection and obtain the channel statusat multiple configured LAA cells. For example, the eNB 160 may determinewhether the channel is busy in a CCA timeslot for a given LAA cell. Ifthe LAA cell is transmitting or the CCA detects another transmission onthe same LAA carrier, then the channel is determined to be busy. The eNB160 may determine that the channel is idle in a CCA timeslot for thegiven LAA cell if the CCA detects no transmission on the same LAAcarrier.

The eNB 160 may perform 1404 channel access and backoff procedures atmultiple configured LAA cells. For example, the eNB 160 may determine abackoff counter value of a given LAA cell based on the CCA detectionresult of the given LAA cell. The eNB 160 may determine whether thebackoff counter is zero or whether the backoff counter is not zero.

The eNB 160 may perform 1406 backoff counter handling if a backoffcounter is not zero. The eNB 160 may perform backoff counter alignmentfor the multiple configured LAA cells based on the backoff countervalue. Therefore, the eNB 160 may align the backoff counters of two ormore LAA cells to the same value.

With backoff counter alignment, the backoff counter of a given LAA cellmay be increased, decreased or maintained the same. In one approach, theeNB 160 may modify (increase or decrease) the backoff counter of a givenLAA cell even if the channel is busy or in a defer period or in abackoff counter count down process. In another approach, the eNB 160 maymodify the backoff counter of a given LAA cell when the backoff counteris within a threshold number of the current backoff counter value.

The eNB 160 may implement one or more different approaches for backoffcounter alignment if the backoff counter is not zero. In a firstapproach, the eNB 160 may perform backoff counter handling if thebackoff counter of the LAA cell is smaller than a threshold value.Therefore, in this approach, the eNB 160 may align the backoff countersof the LAA cells if their backoff counters are smaller than a thresholdnumber.

In a second approach, the eNB 160 may perform backoff counter alignmentonly within LAA cells with the difference of backoff counter valueswithin a given range. Therefore, in this approach, the eNB 160 may alignthe backoff counters of the LAA cells if their backoff counters arewithin a threshold range.

In a third approach, the eNB 160 may perform backoff counter alignmentonly within LAA cells with the same contention window size (CWS). Inother words, the eNB 160 may align the backoff counters of the LAA cellsif they have the same contention window size.

In a fourth approach, the eNB 160 may perform backoff counter alignmentonly within LAA cells that sense the channel in idle state and in abackoff counter count down process. In this approach, the eNB 160 mayfreeze the backoff counter even if the channel is sensed as idle in abackoff counter count down process.

The aligned backoff counter may be determined based on the backoffcounter values of the given LAA cells. In one approach, the alignedbackoff counter may be determined based on the average of the backoffcounter values of the given LAA cells. In another approach, the alignedbackoff counter may be determined based on the minimum backoff countervalue of the given LAA cells. In yet another approach, the alignedbackoff counter may be determined based on the maximum backoff countervalue of the given LAA cells.

In a special case of backoff counter handling, the eNB 160 may groupmultiple LAA cells into an LAA cluster. The eNB 160 may maintain acommon backoff counter for the cluster. Thus, for the LAA cluster, in aCCA timeslot, the channel is sensed as busy if any LAA cell in thecluster senses the channel is busy. The channel is idle if all LAA cellsin the cluster sense the channel is idle.

The eNB 160 may continue 1408 a backoff process after backoff counterhandling. In one approach, the eNB 160 may wait for the channel to beidle for a defer period before resuming a backoff counter count down. Inanother approach, the eNB may continue CCA and a backoff count downprocess with a new backoff counter without inserting a defer period.

FIG. 15 is a flow diagram illustrating yet another method 1500 forscheduling multiple Licensed-Assisted Access (LAA) cells by an eNB 160.The eNB 160 may perform 1502 CCA detection and obtain the channel statusat a configured LAA secondary cell (SCell). For example, the eNB 160 maydetermine whether the channel is busy in a CCA timeslot for a given LAAcell. If the LAA cell is transmitting or the CCA detects anothertransmission on the same LAA carrier, then the channel is determined tobe busy.

The eNB 160 may manage 1504 a counter. For example, the eNB 160 may haveknowledge of the adjacent cells of each LAA node. The eNB 160 may managea backoff counter for each LAA cell.

The eNB 160 may determine 1506 whether the counter is reduced orsuspended if the channel is sensed to be idle. The eNB 160 may determinethat the channel is idle in a CCA timeslot for the given LAA cell if theCCA detects no transmission on the same LAA carrier.

The eNB 160 may reduce 1508 the counter if determined, otherwise the eNB160 may suspend the counter and move to a next channel sensing. The eNB160 may suspend or freeze a backoff counter if the channel is busy or ina defer period or an ICCA period. The eNB 160 may reduce the backoffcounter by one if the channel is idle for an ECCA slot.

The eNB 160 may determine whether or not the eNB 160 performs atransmission, if the counter reaches zero. When the backoff counterreaches 0, the eNB 160 may transmit immediately or defer the LAAtransmission. The eNB 160 may perform the transmission if determined,otherwise the eNB 160 may suspend the transmission and perform anadditional channel sensing for the transmission.

FIG. 16 illustrates various components that may be utilized in a UE1602. The UE 1602 described in connection with FIG. 16 may beimplemented in accordance with the UE 102 described in connection withFIG. 1. The UE 1602 includes a processor 1655 that controls operation ofthe UE 1602. The processor 1655 may also be referred to as a centralprocessing unit (CPU). Memory 1661, which may include read-only memory(ROM), random access memory (RAM), a combination of the two or any typeof device that may store information, provides instructions 1657 a anddata 1659 a to the processor 1655. A portion of the memory 1661 may alsoinclude non-volatile random access memory (NVRAM). Instructions 1657 band data 1659 b may also reside in the processor 1655. Instructions 1657b and/or data 1659 b loaded into the processor 1655 may also includeinstructions 1657 a and/or data 1659 a from memory 1661 that were loadedfor execution or processing by the processor 1655. The instructions 1657b may be executed by the processor 1655 to implement one or more of themethods described above.

The UE 1602 may also include a housing that contains one or moretransmitters 1658 and one or more receivers 1620 to allow transmissionand reception of data. The transmitter(s) 1658 and receiver(s) 1620 maybe combined into one or more transceivers 1618. One or more antennas1622 a-n are attached to the housing and electrically coupled to thetransceiver 1618.

The various components of the UE 1602 are coupled together by a bussystem 1663, which may include a power bus, a control signal bus and astatus signal bus, in addition to a data bus. However, for the sake ofclarity, the various buses are illustrated in FIG. 16 as the bus system1663. The UE 1602 may also include a digital signal processor (DSP) 1665for use in processing signals. The UE 1602 may also include acommunications interface 1667 that provides user access to the functionsof the UE 1602. The UE 1602 illustrated in FIG. 16 is a functional blockdiagram rather than a listing of specific components.

FIG. 17 illustrates various components that may be utilized in an eNB1760. The eNB 1760 described in connection with FIG. 17 may beimplemented in accordance with the eNB 170 described in connection withFIG. 1. The eNB 1760 includes a processor 1755 that controls operationof the eNB 1760. The processor 1755 may also be referred to as a centralprocessing unit (CPU). Memory 1761, which may include read-only memory(ROM), random access memory (RAM), a combination of the two or any typeof device that may store information, provides instructions 1757 a anddata 1759 a to the processor 1755. A portion of the memory 1761 may alsoinclude non-volatile random access memory (NVRAM). Instructions 1757 band data 1759 b may also reside in the processor 1755. Instructions 1757b and/or data 1759 b loaded into the processor 1755 may also includeinstructions 1757 a and/or data 1759 a from memory 1761 that were loadedfor execution or processing by the processor 1755. The instructions 1757b may be executed by the processor 1755 to implement one or more of themethods 200, 700, 800, 900, 1000, 1100, 1400 and 1500 described above.

The eNB 1760 may also include a housing that contains one or moretransmitters 1717 and one or more receivers 1778 to allow transmissionand reception of data. The transmitter(s) 1717 and receiver(s) 1778 maybe combined into one or more transceivers 1776. One or more antennas1780 a-n are attached to the housing and electrically coupled to thetransceiver 1776.

The various components of the eNB 1760 are coupled together by a bussystem 1763, which may include a power bus, a control signal bus and astatus signal bus, in addition to a data bus. However, for the sake ofclarity, the various buses are illustrated in FIG. 17 as the bus system1763. The eNB 1760 may also include a digital signal processor (DSP)1765 for use in processing signals. The eNB 1760 may also include acommunications interface 1767 that provides user access to the functionsof the eNB 1760. The eNB 1760 illustrated in FIG. 17 is a functionalblock diagram rather than a listing of specific components.

FIG. 18 is a block diagram illustrating one implementation of a UE 1802in which scheduling multiple LAA serving cells may be implemented. TheUE 1802 includes transmit means 1858, receive means 1820 and controlmeans 1824. The transmit means 1858, receive means 1820 and controlmeans 1824 may be configured to perform one or more of the functionsdescribed in connection with FIG. 1 above. FIG. 16 above illustrates oneexample of a concrete apparatus structure of FIG. 18. Other variousstructures may be implemented to realize one or more of the functions ofFIG. 1. For example, a DSP may be realized by software.

FIG. 19 is a block diagram illustrating one implementation of an eNB1960 in which scheduling multiple LAA serving cells may be implemented.The eNB 1960 includes transmit means 1917, receive means 1978 andcontrol means 1982. The transmit means 1917, receive means 1978 andcontrol means 1982 may be configured to perform one or more of thefunctions described in connection with FIG. 1 above. FIG. 17 aboveillustrates one example of a concrete apparatus structure of FIG. 19.Other various structures may be implemented to realize one or more ofthe functions of FIG. 1. For example, a DSP may be realized by software.

The term “computer-readable medium” refers to any available medium thatcan be accessed by a computer or a processor. The term“computer-readable medium,” as used herein, may denote a computer-and/or processor-readable medium that is non-transitory and tangible. Byway of example, and not limitation, a computer-readable orprocessor-readable medium may comprise RAM, ROM, EEPROM, CD-ROM or otheroptical disk storage, magnetic disk storage or other magnetic storagedevices, or any other medium that can be used to carry or store desiredprogram code in the form of instructions or data structures and that canbe accessed by a computer or processor. Disk and disc, as used herein,includes compact disc (CD), laser disc, optical disc, digital versatiledisc (DVD), floppy disk and Blu-ray® disc where disks usually reproducedata magnetically, while discs reproduce data optically with lasers.

It should be noted that one or more of the methods described herein maybe implemented in and/or performed using hardware. For example, one ormore of the methods described herein may be implemented in and/orrealized using a chipset, an application-specific integrated circuit(ASIC), a large-scale integrated circuit (LSI) or integrated circuit,etc.

Each of the methods disclosed herein comprises one or more steps oractions for achieving the described method. The method steps and/oractions may be interchanged with one another and/or combined into asingle step without departing from the scope of the claims. In otherwords, unless a specific order of steps or actions is required forproper operation of the method that is being described, the order and/oruse of specific steps and/or actions may be modified without departingfrom the scope of the claims.

It is to be understood that the claims are not limited to the preciseconfiguration and components illustrated above. Various modifications,changes and variations may be made in the arrangement, operation anddetails of the systems, methods, and apparatus described herein withoutdeparting from the scope of the claims.

A program running on the eNB 160 or the UE 102 according to thedescribed systems and methods is a program (a program for causing acomputer to operate) that controls a CPU and the like in such a manneras to realize the function according to the described systems andmethods. Then, the information that is handled in these apparatuses istemporarily stored in a RAM while being processed. Thereafter, theinformation is stored in various ROMs or HDDs, and whenever necessary,is read by the CPU to be modified or written. As a recording medium onwhich the program is stored, among a semiconductor (for example, a ROM,a nonvolatile memory card, and the like), an optical storage medium (forexample, a DVD, a MO, a MD, a CD, a BD, and the like), a magneticstorage medium (for example, a magnetic tape, a flexible disk, and thelike), and the like, any one may be possible. Furthermore, in somecases, the function according to the described systems and methodsdescribed above is realized by running the loaded program, and inaddition, the function according to the described systems and methods isrealized in conjunction with an operating system or other applicationprograms, based on an instruction from the program.

Furthermore, in a case where the programs are available on the market,the program stored on a portable recording medium can be distributed orthe program can be transmitted to a server computer that connectsthrough a network such as the Internet. In this case, a storage devicein the server computer also is included. Furthermore, some or all of theeNB 160 and the UE 102 according to the systems and methods describedabove may be realized as an LSI that is a typical integrated circuit.Each functional block of the eNB 160 and the UE 102 may be individuallybuilt into a chip, and some or all functional blocks may be integratedinto a chip. Furthermore, a technique of the integrated circuit is notlimited to the LSI, and an integrated circuit for the functional blockmay be realized with a dedicated circuit or a general-purpose processor.Furthermore, if with advances in a semiconductor technology, atechnology of an integrated circuit that substitutes for the LSIappears, it is also possible to use an integrated circuit to which thetechnology applies.

Moreover, each functional block or various features of the eNB 160 andthe UE 102 used in each of the aforementioned embodiments may beimplemented or executed by a circuitry, which is typically an integratedcircuit or a plurality of integrated circuits. The circuitry designed toexecute the functions described in the present specification maycomprise a general-purpose processor, a digital signal processor (DSP),an application specific or general application integrated circuit(ASIC), a field programmable gate array signal (FPGA), or otherprogrammable logic devices, discrete gates or transistor logic, or adiscrete hardware component, or a combination thereof. Thegeneral-purpose processor may be a microprocessor, or alternatively, theprocessor may be a conventional processor, a controller, amicrocontroller or a state machine. The general-purpose processor oreach circuit described above may be configured by a digital circuit ormay be configured by an analogue circuit. Further, when a technology ofmaking into an integrated circuit superseding integrated circuits at thepresent time appears due to advancement of a semiconductor technology,the integrated circuit by this technology is also able to be used.

Moreover, each functional block or various features of the base stationdevice and the terminal device used in each of the aforementionedembodiments may be implemented or executed by a circuitry, which istypically an integrated circuit or a plurality of integrated circuits.The circuitry designed to execute the functions described in the presentspecification may comprise a general-purpose processor, a digital signalprocessor (DSP), an application specific or general applicationintegrated circuit (ASIC), a field programmable gate array (FPGA), orother programmable logic devices, discrete gates or transistor logic, ora discrete hardware component, or a combination thereof. Thegeneral-purpose processor may be a microprocessor, or alternatively, theprocessor may be a conventional processor, a controller, amicrocontroller or a state machine. The general-purpose processor oreach circuit described above may be configured by a digital circuit ormay be configured by an analogue circuit. Further, when a technology ofmaking into an integrated circuit superseding integrated circuits at thepresent time appears due to advancement of a semiconductor technology,the integrated circuit by this technology is also able to be used.

What is claimed is:
 1. An evolved NodeB (eNB) for scheduling multipleLicensed-Assisted Access (LAA) cells, comprising: a processor; andmemory in electronic communication with the processor, whereininstructions stored in the memory are executable to: perform clearchannel assessment (CCA) detection and obtain a channel status at aconfigured Licensed-Assisted Access (LAA) secondary cell (SCell); managea counter; determine whether the counter is reduced or suspended if thechannel is sensed to be idle; and reduce the counter if determined,otherwise suspend the counter and move to a next channel sensing.
 2. TheeNB of claim 1, wherein the instructions are further executable to:determine whether or not the eNB performs a transmission, if the counterreaches zero; and perform the transmission if determined, otherwisesuspend the transmission and perform an additional channel sensing forthe transmission.
 3. A method for an evolved NodeB (eNB) for schedulingmultiple Licensed-Assisted Access (LAA) cells, the method comprising:performing clear channel assessment (CCA) detection and obtaining achannel status at a configured Licensed-Assisted Access (LAA) secondarycell (SCell); managing a counter; determining whether the counter isreduced or suspended if the channel is sensed to be idle; and reducingthe counter if determined, otherwise suspending the counter and movingto a next channel sensing.
 4. The method of claim 3, wherein the methodfurther comprises: determining whether or not the eNB performs atransmission, if the counter reaches zero; and performing thetransmission if determined, otherwise suspending the transmission andperforming an additional channel sensing for the transmission.